rk colour inclining
to purple; while that which passes from the left ventricle into the
arteries, is of a bright vermilion hue. The blood which is found in
the pulmonary artery has the same dark purple colour with that in the
vena cava, while that in the pulmonary vein resembles the aortal
blood in its brightness. Hence it would appear, that the blood,
during its passage through the lungs, has its colour changed from a
dark purple to a bright vermilion, in which state it is brought by
the pulmonary vein to the left auricle of the heart; this auricle,
contracting, expels the blood into the corresponding ventricle, by
whose action, and that of the arteries, it is distributed to all
parts of the body. When it returns, however, by the veins, it is
found to have lost its fine bright colour. It would appear,
therefore, that the blood obtains its red colour during its passage
through the lungs, and becomes deprived of it during its circulation
through the rest of the body.

That the blood contains iron, may be proved by various experiments:
if a quantity of blood be exposed to a red heat in a crucible, the
greatest part will be volatilised and burnt; but a quantity of brown
ashes will be left behind, which will be attracted by the magnet. If
diluted sulphuric acid be poured on these ashes, a considerable
portion of them will dissolve; if into this solution we drop tincture
of galls, a black precipitate will take place, or if we use prussiate
of potash, a precipitate of prussian blue will be formed. These facts
prove, beyond doubt, that a quantity of iron exists in the blood.

I shall not now particularly inquire how it comes there; it may
partly be taken into the blood along with the vegetable and animal
food, which is received into the stomach; for the greatest part of
the animal and vegetable substances, which we receive as food,
contain a greater or less quantity of iron. Or it may be partly
formed by the animal powers, as would appear from the following
circumstance. The analysis of an egg, before incubation, affords not
the least vestige of iron, but as soon as the chick exists, though it
has been perfectly shut up from all external communication, if the
egg be burnt, the ashes will be attracted by the magnet.

But, however we may suppose the blood to obtain its iron, it
certainly does contain it; if the coagulable lymph and serum of the
blood be carefully freed from the red particles, by repeated washing,
the stricte